SOLVENTS OF ORGANIC CARRIERS FOR ELECTRONIC PASTES
Organic carrier is basic material of electronic pastes. They are identified as volatility carrier and non-volatility carrier. As the volatility performance, this specification influence rheology and initial adhesive attraction to electronic pastes.
There are some typical carriers be used in formulas, include Ethyl Cellulose (EC), Nitrated Cellulose (NC), PVA, PAA, polyurethane emulsion (PUE), PVB, PAM, etc. Binders usually use Pine Oil, Turpentine, EC-terpineol and Acrylic Resins. In these binders, EC-terpineol is the main stabilizer-solvent system. (Shiyong Luo, 2007) The viscosity of electronic pastes was controlled by Ethyl Cellulose on mass fraction. As tests resulted that when the EC is about 5%, the formula works well.
In the stabilizer-solvent system, we often consider the effect of volatility to solvent formulas. Pure solvent formulas often show a high volatilization, this feature makes unsteadiness on pastes.
A high speed volatilization will increase the viscosity, reduce rheology that screen be easy blocking. A too slow performance will delay the painting process, and inks would not easy drying that produce rejected. If the volatility focus on a range of temperature, the film chaps and produces air hole after the paste sinter. (Shiyong Luo, 2006)
So how to choose the right solvent is the key to improve the performance of electronic pastes.
Electronic pastes are conducting by conductive particles. The based resin types, grainsize and contents of metal ingredients, each factors will influence the conductibility. (Dandan Wu, 2008) Terpineol is the main solvent, dissolves tackifiers and organic ingredients.
- CUT FORCE
The paste formulas must be satisfied the customer demands. Different of manufacturers have their specification in adhesion and tenacity. Adhesion ability of electronic pestes rest with based resin and innerstress of contact surface. If the innerstress perform a too high level, the thermal coefficient of expansion will not satisfied in semiconductor devices.
Some research results that the contents of organic carrier in electronic paste formulas will effects the cut force. ( Weiping Gan, 2007) When the contents of carrier increasing, the cut force of sinter film will reduce due to the shrinkage ratio. If formulas can improve this shrinkage ratio, it can improve the compactability in the film. But if organic carrier contents too low, the paste will blocks screen.
Discuss the Volatility of Solvents
The volatilization loss of pure solvent formulas were higher than complex solvent formulas. Due to the different of boiling points of pure solvents, which always easy volatilizing the carriers. If we choose complex solvent, control the volatilization performance through adjust contents of volatile substances, such as Turpentine, Terpineol, Diethylene glycol monobuthyl ether acetate (DBAC) or Dibutyl phthalate (DBP). The organic carriers show a character of pseudoplastic fluid and reduce volatilization loss.
In the EC-terpineol stabilizer-solvent system, we can improve the volatilization feature by add Turpentine, Terpineol, DBAC or DBP. There is a referrible proportion is DBAC by 28.5%, Terpineol by 57%, DBP by 9.5% and Ethyl Cellulose by 5%. (Shiyong Luo, 2006)
The mass loss of Ethyl Cellulose was 91.66% at 325°C to 375°C. Carrier was volatilized at the temperature range of 150°C to 200°C, the mass loss was 93.88%.
Figure 1. Thermo gravimetric curves of the Ethyl cellulose and the organic carrier. Source: Volatility of Organic Vehicle for Electronic Paste, Shiyong Luo, 2006
Figure 2. The volatilization loss of pure solvents after being kept at a fixed temperature for 20min. Source: Volatility of Organic Vehicle for Electronic Paste, Shiyong Luo, 2006
Figure 3. The volatilization loss of complex solvents and the organic carrier after being kept at a fixed temperature for 20min. Source: Volatility of Organic Vehicle for Electronic Paste, Shiyong Luo, 2006
Innovation & Market Forecast
- E-inks market value
- Printed electronics market value
Printed electronics & Electronic Inks Industry
Photovoltaic Pastes Maket
The main photovoltaic pastes are back Ag paste, silverback paste and front silver paste. According as the forcecast to photovoltaic installation on 2015, the market volume of Ag paste was 30k tons, Silver paste was 160k tons. The total volume of Chinese market in the world by 36%. (Source: xincailiao.com)
- Silver Paste
- Ag Paste
- Reduce manufacture cost, use BME replace to NME.
- Improve performance.
- Eco friendly, limited to use BBP, DBP and unleaded formulas will are the industry standard.
- %, MSB Efficiency
- Silver Paste Consumption, KG